MEMS device with differential vertical sense electrodes

ABSTRACT

A MEMS device includes a first sense electrode and a first portion of a sense mass formed in a first structural layer, where the first sense electrode is fixedly coupled with the substrate and the first portion of the sense mass is suspended over the substrate. The MEMS device further includes a second sense electrode and a second portion of the sense mass formed in a second structural layer. The second sense electrode is spaced apart from the first portion of the sense mass in a direction perpendicular to a surface of the substrate, and the second portion of the sense mass is spaced apart from the first sense electrode in the same direction. A junction is formed between the first and second portions of the sense mass so that they are coupled together and move concurrently in response to an imposed force.

TECHNICAL FIELD OF THE DISCLOSURE

The present disclosure relates generally to microelectromechanicalsystems (MEMS) devices. More specifically, the present disclosurerelates to MEMS devices with differential vertical sense electrodes forZ-axis sensing.

BACKGROUND OF THE DISCLOSURE

Microelectromechanical Systems (MEMS) sensor devices are widely used inapplications such as automotive, inertial guidance systems, householdappliances, protection systems for a variety of devices, and many otherindustrial, scientific, and engineering systems. Such MEMS devices areused to sense a physical condition such as acceleration, angular rate,pressure, or temperature, and to provide an electrical signalrepresentative of the sensed physical condition. Capacitive-sensing MEMSsensor designs are highly desirable for operation in high gravityenvironments and in miniaturized devices, and due to their relativelylow cost.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present disclosure may be derivedby referring to the detailed description and claims when considered inconnection with the Figures, wherein like reference numbers refer tosimilar items throughout the Figures, the Figures are not necessarilydrawn to scale, and:

FIG. 1 schematically shows a top view of a MEMS device in accordancewith an embodiment;

FIG. 2 shows a side view of the MEMS device along section line 2-2 shownin FIG. 1;

FIG. 3 shows a side view of the MEMS device along section line 3-3 shownin FIG. 1;

FIG. 4 shows a stylized side view of the MEMS device of FIG. 1 alongsection line 2-2 in which a movable element of the MEMS device has movedin response to an imposed force;

FIG. 5 shows a stylized side view of the MEMS device of FIG. 1 alongsection line 3-3 in which the movable element of the MEMS device hasmoved in response to an imposed force;

FIG. 6 shows a top view of a MEMS device in accordance with anotherembodiment;

FIG. 7 shows a side view of the MEMS device along section line 7-7 shownin FIG. 6;

FIG. 8 shows a side view of the MEMS device along section line 8-8 shownin FIG. 6;

FIG. 9 shows a partial side view of the MEMS device along section line9-9 shown in FIG. 6;

FIG. 10 shows a flowchart of a microelectromechanical systems (MEMS)device fabrication process in accordance with another embodiment;

FIG. 11 shows a partial side view of an exemplary structure at abeginning stage of processing fabricated in accordance with the MEMSdevice fabrication process;

FIG. 12 shows a partial side view of the exemplary structure from FIG.11 at a subsequent stage of processing;

FIG. 13 shows a partial side view of the exemplary structure from FIG.12 at a subsequent stage of processing;

FIG. 14 shows a partial side view of the exemplary structure from FIG.13 at a subsequent stage of processing;

FIG. 15 shows a partial side view of the exemplary structure from FIG.14 at a subsequent stage of processing;

FIG. 16 shows a partial side view of the exemplary structure from FIG.15 at a subsequent stage of processing;

FIG. 17 shows a partial side view of the exemplary structure of FIG. 16at a subsequent stage of processing;

FIG. 18 shows a partial side view of the exemplary structure from FIG.17 at a subsequent stage of processing;

FIG. 19 shows a partial side view of the exemplary structure from FIG.18 at a subsequent stage of processing;

FIG. 20 shows a partial side view of another exemplary structure at abeginning stage of processing fabricated in accordance with the MEMSdevice fabrication process;

FIG. 21 shows a partial side view of the exemplary structure from FIG.20 at a subsequent stage of processing;

FIG. 22 shows a partial side view of the exemplary structure from FIG.21 at a subsequent stage of processing;

FIG. 23 shows a partial side view of the exemplary structure from FIG.22 at a subsequent stage of processing;

FIG. 24 shows a partial side view of the exemplary structure from FIG.23 at a subsequent stage of processing;

FIG. 25 shows a partial side view of the exemplary structure from FIG.24 at a subsequent stage of processing; and

FIG. 26 shows a partial side view of the exemplary structure from FIG.25 at a subsequent stage of processing.

DETAILED DESCRIPTION

The fabrication and packaging of MEMS device applications, as well asstresses resulting from soldering the packaged MEMS device onto aprinted circuit board in an end application, can cause the non-uniformstretching, bending, or warping across a surface of the substrate uponwhich the MEMS device is formed. Substrate curvature can cause changesin the sense signal, thus adversely affecting the output performance ofthe MEMS device.

A number of MEMS inertial sensors, such as accelerometer and angularrate sensor devices, implement vertical sensing, i.e., sensing that isperpendicular to the plane of the substrate. A commonly implementedstructure for MEMS device vertical sensing is a “teeter-totter” sensemass configuration that is capable of rotating above a substrate underz-axis force. Fixed positive and negative sense electrodes can bearranged below the teeter-totter sense mass on opposing sides of an axisof rotation of the sense mass. The sense mass will tilt or rotate aboutthe axis of rotation in response to a force, thus changing its positionrelative to the fixed sense electrodes. This change in position resultsin capacitance signals whose difference, i.e., a differentialcapacitance, is indicative of the force.

This style of vertical sensing can be problematic in that the size ofthe sense gaps between the sense mass and each of the sense electrodesare highly sensitive to substrate curvature because the sense electrodesare separated by a relatively long distance in the plane of thesubstrate. For example, the sense electrodes may be located on opposingsides of the axis of rotation. Secondly, the teeter-totter style ofvertical sensing can result in common mode displacement, wherein theentire sense mass moves generally perpendicular to the plane of thesubstrate, instead of tilting. Since the sense gaps, i.e., one gapbetween the sense mass and the positive sense electrode and another gapbetween the sense mass and the negative sense electrode, are located onthe same side of the sense mass, the common mode displacement can causeboth the positive and the negative sense signals to change equally,resulting in no net differential signal. Thus, a change in the size ofthe sense gaps due to common mode displacement can introduce a scalefactor change, and potentially adversely shift the sensitivity of thedevice. A change in the sense gap size due to common mode displacementcan also alter the sense frequency of the device, essentially frequencytuning through electrostatic spring softening. In general, frequencytuning is a change in the resonant frequency of a sense oscillator,e.g., sense mass, due to an applied electrostatic force. Thus, theresonant frequency may change if the size of the gaps between the sensemass and the electrodes supplying the electrostatic force change. Thus,what is needed is a MEMS sensor device with a robust vertical senseelectrode design that is less sensitive to substrate curvature and harshaccelerations.

Some embodiments disclosed herein entail microelectromechanical systems(MEMS) devices that include two structural layers, and junctionsconnecting elements of the two structural layers. The two structurallayers are subsequently mechanically released, or detached, from theunderlying substrate. Accordingly, a movable sense mass (a portion ofwhich is formed in each of the two structural layers) is interleavedboth below one fixed electrode and above a separate fixed electrode.This enables differential sensing such that any signal componentresulting from the common mode displacement will effectively cancel.Another embodiment entails a method for fabricating the MEMS deviceusing two structural layers, in which portions of the two structurallayers are not in direct contact with the underlying substrate, and inwhich each structural layer has sense capability of an opposing polarityso as to provide a differential configuration.

Referring now to FIGS. 1-3, FIG. 1 schematically shows a top view of aMEMS device 20 in accordance with an embodiment. FIG. 2 shows a sideview of MEMS device 20 along section line 2-2, and FIG. 3 shows a sideview of MEMS device 20 along section line 3-3. FIGS. 1-3 are illustratedusing various shading and/or hatching to distinguish the differentelements produced within the structural layers of MEMS device 20, aswill be discussed below. These different elements within the structurallayers may be produced utilizing current and upcoming surfacemicromachining techniques of depositing, patterning, etching, and soforth. Accordingly, although different shading and/or hatching isutilized in the illustrations, the different elements within thestructural layers are typically formed out of the same material, such aspolysilicon, single crystal silicon, and the like.

The elements of MEMS device 20 (discussed below) may be describedvariously as being “attached to,” “attached with,” “coupled to,” “fixedto,” or “interconnected with,” other elements of MEMS device 20.However, it should be understood that the terms refer to the direct orindirect physical connections of particular elements of MEMS device 20that occur during their formation through patterning and etchingprocesses of MEMS fabrication, as will be discussed in connection withFIG. 9.

MEMS device 20 includes a substrate 22, a structural layer 24, and astructural layer 26 that is spaced apart from structural layer 24. Anumber of elements are formed in structural layer 24. In an embodiment,these elements include at least one sense electrode 28, a portion 30 ofa movable sense mass 32, and a fixed element 34. Likewise, a number ofelements are formed in structural layer 26. In an embodiment, theseelements include at least one sense electrode 36 (two of which areshown) and another portion 38 of movable sense mass 32. Together,portions 30 and 38 form movable sense mass 32, as will be discussed ingreater detail below. Sense electrodes 36 in structural layer 26 arerepresented by upwardly and rightwardly directed narrow hatching, andportion 38 of sense mass 32 in structural layer 26 is represented bydownwardly and rightwardly directed narrow hatching to distinguishelements 36 and 38 in structural layer 26 from those elements formed inthe underlying structural layer 24.

Sense electrode 28 in structural layer 24 is fixedly coupled to asurface 40 of substrate 22 by an anchor 42. Likewise, fixed element 34in structural layer 24 is fixedly coupled to surface 40 of substrate 22by an anchor 43. MEMS device 20 further includes an anchor element 44and compliant members 46 formed in structural layer 24. Anchor element44 is fixedly coupled to surface 40 of substrate 22 by an anchor 48, andcompliant members 46 are interconnected between portion 30 of sense mass32 and anchor element 44. Anchor 42 is depicted in FIGS. 1 and 2 by an“X” enclosed in a box to emphasize the attachment of a particularelement, and in this case sense electrode 28, with the underlyingsubstrate 22. Similarly, anchors 43 and 48 are depicted in FIG. 1 by an“X” enclosed in a box to emphasize the fixed attachment of fixed element34 and anchor element 44 with the underlying substrate 22. In anembodiment, anchors 42, 43, and 48 may be formed when a portion of asacrificial layer 50 remains beneath structural layer 24 followingetching of sacrificial layer 50 during processing (discussed below).

In contrast to the fixed attachment of sense electrode 28, fixed element34, and anchor element 44 with substrate 22, portion 30 of movable sensemass 32 in structural layer 24 is suspended over surface 40 of substrate22 so that a gap 52 is present between surface 40 and portion 30 ofsense mass 32. In an embodiment, compliant members 46 are connected toan outer edge 54 of portion 30 such that portion 30 of sense mass 32 isa cantilevered structure overlying surface 40 of substrate 22 that issupported only at one side.

Portion 30 of sense mass 32 further includes an opening 56 extendingthrough a thickness 58 of portion 30, and sense electrode 28 resideswithin opening 56. Opening 56 is sized such that a gap 60 is formedbetween portion 30 and sense electrode 28. In some embodiments, opening56 also extends laterally from an outer edge 62 of portion 30 such thatportion 30 of sense mass 32 is a generally U-shaped member. Fixedelement 34 is spaced away from outer edge 62 so that a gap 64 is alsoformed between fixed element 34 and the adjacent sense electrode 28 andportion 30 of sense mass 32.

In some embodiments, a shield 66 is located in gaps 60 and 62. Thus,shield 66 is interposed between sense electrode 28 and portion 30 ofsense mass 32. Additionally, shield 66 is interposed between fixedelement 34 and each of sense electrode 28 and portion 30 of sense mass32. Shield 66 electrically isolates sense electrode 28 from thesurrounding portion 30 of sense mass 32 to largely prevent motionsensitive capacitance from being created between portion 30 and senseelectrode 28. Shield 66 is represented in FIGS. 1 and 3 by a stippledpattern to distinguish it from surrounding structures.

In some embodiments, shield 66 extends to an outside region 68 of MEMSdevice 20 and is coupled to corresponding shield anchors 70. Thus,shield 66 may be suspended over surface 40 of substrate 22. Again,shield anchors 70 are depicted in FIG. 1 by an “X” enclosed in a box toemphasize the fixed attachment of shield anchors 70 with the underlyingsubstrate 22. Those skilled in the art will recognize that shield 66 andshield anchors 70 may be arranged differently than that which is shown.

Junctions 72, 74 are formed between portion 30 of sense mass 32 formedin structural layer 24 and portion 38 of sense mass 32 formed instructural layer 26. That is, junctions 72, 74 are structural featuresthat couple, or join, portion 30 with portion 38 to form movable sensemass 32. Junction 72 is positioned on one side 76 of opening 56 andjunction 74 is positioned on an opposing side 78 of opening 56. The pairof junctions 72, 74 couple portion 38 with portion 30 so that portion 38of sense mass 32 spans across a width 80 of opening 56 and thereforeoverlies sense electrode 28. Junctions 72 and 74 extend above portion 30of sense mass 32. As such, a sense gap 82 (visible in FIG. 2) is formedbetween portion 38 of sense mass 32 and the underlying sense electrode28 and portion 38 of sense mass 32. In FIG. 1, junctions 72, 74 aredepicted by dark downwardly and rightwardly directed narrow hatching todistinguish them from portion 38, as well as to emphasize their couplingbetween portions 30 and 38 to form sense mass 32.

Junctions 84, 86 are also formed between fixed element 34 formed instructural layer 24 and sense electrodes 36 formed in structural layer26. That is, junctions 84, 86 are structural features that couple, orjoin, fixed element 34 with each of sense electrodes 36. In anembodiment, junction 84 couples fixed element 34 with one of senseelectrodes 36, and junction 86 couples fixed element 34 with the otherone of sense electrodes 36. Junctions 84, 86 extend above fixed element34. As such, sense gaps 88 (one of which is visible in FIG. 3) is formedbetween the underlying portion 30 of sense mass 32 and each of senseelectrodes 36. In FIG. 1, junctions 84, 86 are depicted by dark upwardlyand rightwardly directed narrow hatching to distinguish them from senseelectrodes 36, as well as to, emphasize their coupling between fixedelement 34 and sense electrodes 36.

In the illustrated embodiment, MEMS device 20 may be an accelerometerhaving capacitive sensing capability. In general, compliant members 46suspend sense mass 32 over substrate 22 in a neutral position generallyparallel to substrate 22 until the selective application of force, dueto some other means, causes a deflection thereof. By way of example,sense mass 32 of MEMS device 20 moves when MEMS device 20 experiencesacceleration in a Z-direction 90 that is generally perpendicular tosurface 40 of substrate 22. Accordingly, compliant members 46 enablesense mass 32 to rotate, or tilt, about an axis of rotation 92 that isoffset away from portion 30 of sense mass 32. Since portions 30, 38 arecoupled via junctions 72, 74, compliant members 46 enable concurrentmovement of portions 30, 38 of sense mass 32. The tilting motion ofsense mass 32 may be detected by sense electrodes 28, 38 interleavedwith sense mass 32. This movement can subsequently be converted viaelectronics (not shown) into a signal having a parameter magnitude (e.g.voltage, current, frequency, etc.) that is dependent on theacceleration. In this example, MEMS device 20 may be a single axisaccelerometer for detection of acceleration in Z-direction 90. However,alternative embodiments may entail dual axis accelerometers or otherMEMS sensing devices.

Referring to FIGS. 4-5, FIG. 4 shows a stylized side view of MEMS device20 along section line 2-2 of FIG. 1 in which sense mass 32 has moved inresponse to an imposed force 92 in Z-direction 90. FIG. 5 shows astylized side view of MEMS device 20 along section line 3-3 of FIG. 1 inwhich sense mass 32 of MEMS device 20 has moved in response to imposedforce 92. Accordingly, FIGS. 4 and 5 represent a condition in whichforce 92 was sufficient to cause sense mass 32 to rotate about axis ofrotation 92. This rotational motion is represented by an arrow 94 inFIG. 5 about axis of rotation 92, which is represented as a point inFIG. 5. Gap 52 below the suspended sense mass 32 provides the requisitespace to allow for movement of sense mass 32. However, in someembodiments (not shown), it may be possible to form additionalelectrodes on surface 40 of substrate 22 to provide additional sensingor for other purposes such as shielding or control electrodes.

The particular formation of elements within the two structural layers24, 26 and suitable connections of the elements via junctions 72, 74,84, and 86 yields a structural configuration in which sense mass 32 isinterleaved with sense electrodes 28, 36. That is, portion 30 of sensemass 32 is located below sense electrodes 36 and portion 38 of sensemass 30 is located above sense electrode 28 in Z-direction 90.Furthermore, sense electrodes 28, 36 are located on the same side ofaxis of rotation 92, with axis of rotation 92 being offset away fromsense mass 32. Accordingly, when sense mass 32 rotates about axis ofrotation 92, the width of sense gaps 82, 88 will change the same amountbut in opposite directions.

In the illustrations of FIGS. 4 and 5, rotational motion (represented byarrow 94) of sense mass 32 resulting from the imposed force 92 causessense gap 82 to get smaller and sense gap 88 to get larger. Therefore, asense capacitance signal 96, labeled C1, between portion 38 of sensemass 32 and sense electrode 28 will decrease, and a sense capacitancesignal 98, labeled C2, between portion 30 of sense mass 32 and senseelectrodes 36 will increase. Accordingly, sense signals 96 and 98 are ofopposite polarity. Furthermore, sense gaps 82 and 88 change by the samemagnitude due to their location on the same side of axis of rotation 92thus producing differential sensing and substantially reducing theelectrostatic force imbalance generated from a bias voltage applied andcommon mode motion being induced through package deformations.

In addition, a vertical sense system in which sense gaps 82 and 88 areproduced on the same side of axis of rotation 92 can alleviate the needfor a traditional teeter-totter type sense mass for a Z-axisaccelerometer. A traditional teeter-totter style sense mass may be lessefficient in terms of size than the vertical sense system describedabove due to the need for inclusion of a “heavy side” of the sense mass.Accordingly, the vertical sense system of MEMS device 20 achievessavings in area relative to traditional teeter-totter style sensemasses. Furthermore, since sense electrodes 28 and 36 are in closeproximity to one another on the same side of axis of rotation 92 theycan compensate for package stress through effective cancellation ofsignal component due to common mode displacement. Accordingly, thevertical sense system of MEMS device 20 provides a differential, robust,and space efficient design for accelerometers, angular rate sensors, orany of various sensors that have vertical sensing capability.

In alternative embodiments, the vertical sense system of MEMS device 20may be implemented in a conventional teeter-totter sensor by adding thevertical sense system on both sides of the axis of rotation, with one ofthe sides including a heavy end. Such a teeter-totter structuralconfiguration would have portions of sense capacitance signal 96 andsense capacitance signal 98 on both sides of the axis of rotation, andmay be more immune to package deformations and common mode motions thana conventional teeter-totter sensor. Additionally, or alternatively, theconfiguration of an interleaved vertical sense system does notnecessarily require a tipping or teeter-totter type of movable element,but could instead enable differential sensing in a pure vertical motionsensor in which the proof mass moves in a more trampoline-like motion.

Referring now to FIGS. 6-9, FIG. 6 shows a top view of a MEMS device 100in accordance with another embodiment. FIG. 7 shows a side view of MEMSdevice 100 along section line 7-7 of FIG. 6. FIG. 8 shows a side view ofMEMS device 100 along section line 8-8 of FIG. 6, and FIG. 9 shows apartial side view of MEMS device 100 along section line 9-9 of FIG. 6.In an embodiment, MEMS device 100 implements a vertical sense system inan angular rate sensor, or gyroscope, configuration.

MEMS device 100 generally includes at least one drive mass 102 (two inthe illustrated embodiment) and at least one vertical sensing structure104 (two in the illustrated embodiment) spaced apart from an underlyingsubstrate 106. A number of elements of each vertical sensing structure104 are formed in each of two structural layers 107 and 109. In anembodiment, vertical sensing structure 104 includes at least one senseelectrode 108 and a portion 110 of a movable sense mass 112 formed instructural layer 107, and at least one sense electrode 114 and anotherportion 116 of movable sense mass 112 formed in structural layer 109.Together, portions 110 and 116 form movable sense mass 112.

MEMS device 100 further includes anchor elements 120 and compliantmembers 122 formed in structural layer 109. Anchor elements 120 arefixedly coupled to a surface 124 of substrate 106 by an attachmentmaterial, referred to herein as an anchor 126, and compliant members 122are interconnected between each of drive masses 102 and anchor elements120. Anchors elements 126 are depicted in FIGS. 6 and 7 by an “X”enclosed in a box to emphasize the attachment of a particular element,and in this case drive masses 102 with the underlying substrate 106 viacompliant members 122 and anchor elements 120. However, as shown, drivemasses 102 are spaced apart from, i.e., suspended above, surface 124 ofsubstrate 106.

In some embodiments, MEMS device 100 includes additional anchor elements128, compliant members 129, and a beam in the form of a torsion flexure130 formed in structural layer 109. Anchor elements 128 are fixedlycoupled to surface 124 of substrate 106 by an attachment material,referred to herein as an anchor 132. Compliant members 129 are connectedto the two vertical sense structures 104 and to torsion flexure 130.Compliant members 129 enable relatively large movement of sense masses112 along X-axis 164. Torsion flexure 130 is spaced apart from substrate106 and is interconnected between anchor elements 128. Torsion flexure130 allows rotation of the suspended elements about Y-axis 162.Therefore, torsion flexure 130 enables rocking movement of sense masses112 in response to angular velocity, as will be discussed in greaterdetail below. Again, anchors 132 are depicted in FIG. 6 by an “X”enclosed in a box to emphasize their attachment with the underlyingsubstrate 106.

Now with regard to the elements of each vertical sensing structure 104,each of sense electrodes 108 in structural layer 107 is fixedly coupledto substrate 106 by an attachment material, referred to herein as ananchor 134. In addition, a fixed element region 136 of each senseelectrode 114 is coupled to surface 124 of substrate 106 via anattachment material, referred to herein as an anchor 138. Thus, each ofsense electrodes 114 formed in structural layer 109 is a cantileveredstructure overlying surface 124 of substrate 106 that is supported onlyat one side. Again, anchors 134 and 138 are depicted in FIGS. 6, 8, and9 by an “X” enclosed in a box to emphasize their fixed attachment withthe underlying substrate 106. However, although fixed element region 136is attached with the underlying substrate 106, the remainder of each ofsense electrodes 114 is spaced apart from, i.e., suspended abovesubstrate 106, as particularly evident in FIG. 7. In an embodiment,anchors 126, 132, 134, and 138 may be formed when a portion of asacrificial layer 140 remains beneath structural layer 107 followingetching of sacrificial layer 140 during processing (discussed below).

In contrast to the fixed attachment of sense electrodes 108 withsubstrate 106, portions 110 of sense masses 112 in structural layer 107are suspended over surface 124 of substrate 106 so that gaps 142(visible in FIGS. 7 and 9) are present between surface 124 and portions110 of sense masses 112. Junctions 144 are formed between portions 110of sense masses 112 formed in structural layer 107 and portions 116 ofsense masses 112 formed in structural layer 109. That is, junctions 144are structural features that couple, or join, portion portions 110 withportions 112 to form each of the two movable sense masses 112 of MEMSdevice 100. This structural feature is particularly visible in FIGS. 6and 7 and is distinguished by rightwardly and downwardly directed narrowhatching. As such, sense gaps 146 (visible in FIGS. 7 and 9) are formedbetween sense electrodes 114 and the underlying portions 110 of sensemasses 112. Additionally, sense gaps 148 (visible in FIGS. 8 and 9) areformed between portions 116 of sense mass 112 and the underlying senseelectrodes 108.

As shown in FIG. 6, each portion 116 of each sense mass 112 includes anopening 150 extending through a thickness of each portion 116, and oneof sense electrodes 114 resides within each opening 150. Like MEMSdevice 20 (FIG. 1), each opening 150 is sized such that a gap 152 isformed between each portion 116 and its corresponding sense electrode114. Furthermore, in some embodiments, each opening 150 also extendslaterally from an outer edge 154 of each portion 116 such that eachportion 116 is a generally U-shaped member. Although not shown forsimplicity, a shield may largely surround each of sense electrodes 114,as discussed in detail above in connection with shield 66 (FIG. 1).

In the illustrated embodiment, MEMS device 100 may be an angular ratesensor, also known as a gyroscope, having capacitive sensing capability.Each of drive masses 102 includes an opening 156 extending through athickness of structural layer 109. One of portions 116 of one of sensemasses 112 resides within each opening 156. Each portion 116 of eachsense mass 112 may be coupled to an associated drive mass 102 viacompliant members 158 that are fairly stiff in an X-direction butcompliant in a Z-direction to allow each of sense masses 112 to tilt orrotate about an axis of rotation. Those skilled in the art willrecognize that compliant members 158 may have great variation in sizeand shape from that which is stylistically shown in FIG. 6.

In an exemplary embodiment, MEMS device 100 is generally configured tosense angular rate when MEMS device 100 is subjected to angular velocityabout the Y-axis in a three-dimensional coordinate system, referred toherein as an input axis 162. By convention, MEMS device 100 isillustrated as having a generally planar structure within an X-Y plane166 defined by an X-axis 164 and Y-axis 162, wherein a Z-axis 168extends out of the page, normal to X-Y plane 166 in FIG. 6 and Z-axis168 extends upwardly and downwardly in FIGS. 7-9.

To operate MEMS device 100, a drive system (not shown) in communicationwith drive masses 102 enables linear mechanical oscillation of drivemasses 102 within X-Y plane 166. Accordingly, drive masses 102 willlinearly oscillate along, i.e. substantially parallel to X-axis 164.Sense masses 112 also linearly oscillate along X-axis 164 due to thehigh stiffness of compliant members 158 to this motion. The oscillatorydrive motion may be kept constant to maintain constant sensitivity ofMEMS device 100. Additionally or alternatively, the frequency ofoscillation can be locked to the mechanical resonance of drive masses102 to minimize drive power.

Once sense masses 112 are put into linear oscillatory motion alongX-axis 164, they are capable of detecting an angular rate, i.e., angularvelocity, induced by MEMS device 100 being rotated about input axis 162,i.e., the Y-axis. As MEMS device 100 experiences an angular velocityabout input axis 162, sense masses 112 rock, tilt, rotate, or otherwiseoscillate together about Y-axis 162 via torsion flexure 130, asrepresented by a bi-directional arrow 169. In this example, theout-of-plane sense motion of sense masses 112 is in the directionsubstantially parallel to Z-axis 168. Since portions 110 and 116 ofsense mass 112 are coupled via junctions 144, torsion flexure 130enables concurrent movement of portions 110 and 116 of sense mass 112.This movement can subsequently be converted via electronics (not shown)into a signal having a parameter magnitude (e.g., voltage, current,frequency, etc.) that is dependent upon the angular rotation rate ofMEMS device 100 about input axis 164, i.e., the Y-axis.

The suitable formation of elements within the two structural layers 107and 109 and suitable connection of portions 110 and 116 of sense masses112 via junctions 144 yields a structural configuration in which sensemass 112 is interleaved with sense electrodes 108 and 114. That is,portions 110 of sense masses 112 are located below sense electrodes 114,and portions 116 of sense masses 112 are located above sense electrodes108.

Accordingly, in FIG. 7, a sense capacitance signal 170, labeled C1,between portion 110 of sense mass 112 and sense electrode 114 willchange by the same magnitude as a sense capacitance signal 172, labeledC2, between portion 112 of sense mass 112 and sense electrode 114.Likewise, in FIG. 8, sense capacitance signal 170, labeled C1, betweenportion 116 of sense mass 112 and sense electrode 108 will change by thesame magnitude as sense capacitance signal 172, labeled C2, betweenportion 116 of sense mass 112 and sense electrode 108 due to theirlocation on the same side of the axis of rotation, i.e., X-axis 164.However, sense signals 170 and 172 are of opposite polarity.Furthermore, sense gaps 146 and 148 change by the same magnitude due totheir location on the same side of axis of rotation 162 thus producingdifferential sensing and cancellation of electrostatic forces from, forexample, common mode displacement.

FIG. 10 shows a flowchart of a microelectromechanical systems (MEMS)device fabrication process 200 in accordance with another embodiment.MEMS device fabrication process 200 provides generalized methodology forMEMS device 20 (FIG. 1) and/or MEMS device 100 (FIG. 6) using twostructural layers to form a sense mass interleaved with the senseelectrodes so as to produce a vertical differential sense capability.MEMS device fabrication process 200 will be discussed in connection withthe fabrication of MEMS device 20, and reference will be made to FIGS.11-19 which show a portion of an exemplary structure at various stagesof fabrication in accordance with process 200. Thereafter, MEMS devicefabrication process 200 will be discussed in connection with thefabrication of MEMS device 100, and reference will be made to FIGS.20-26 which show a portion of another exemplary structure at variousstages of fabrication in accordance with process 200. It should becomeapparent that the following methodology can be adapted to fabricateother MEMS device designs with vertical differential sense capabilityfabricated within two structural layers.

Fabrication process 200 is described below in connection with thefabrication of a single MEMS device 20 or 100 for simplicity ofillustration. However, it should be understood by those skilled in theart that the following process allows for concurrent manufacturing of aplurality of MEMS devices. For example, multiple MEMS devices mayundergo concurrent semiconductor thin-film manufacturing on a substrate.The individual MEMS devices can then be cut, or diced, in a conventionalmanner to provide individual MEMS devices that can be packaged andcoupled onto a printed circuit board in an end application.

MEMS device fabrication process 200 begins with an activity 202. Atactivity 202, substrate 22 is provided with sacrificial layer 50deposited thereon.

Referring to FIG. 11 in connection with activity 202, FIG. 11 shows aside view of an exemplary structure 204 in a beginning stage 205 ofprocessing in accordance with activity 202. At beginning stage 205,substrate 22 is provided. In an embodiment, process 200 may implementsilicon on insulator (SOI) technology which uses a layeredsilicon-insulator-silicon wafer 206 in lieu of a conventional siliconsubstrate. Accordingly, substrate 22 may be the bottommost silicon layerwithin wafer 206, sacrificial layer 50 may be the intervening insulatorlayer of wafer 206, and structural layer 24 may be the topmost siliconlayer within wafer 206. Sacrificial layer 50 is represented by a darkstippled pattern in FIG. 11, and each of substrate 22 and structurallayer 24 are represented by a light stippled pattern in FIG. 11. Thoseskilled in the art will recognize that in alternative embodiments, aconventional silicon substrate may be utilized for substrate 22, uponwhich sacrificial layer 50 may be deposited, followed by formation ofstructural layer 24 overlying sacrificial layer 50.

With reference back to MEMS device fabrication process 200 (FIG. 10),following activity 202, an activity 208 is performed. At activity 208,structural layer 24 (FIG. 2) is suitably formed over sacrificial layer50 (FIG. 2) to produce at least sense electrode 28, portion 30 of sensemass 32, fixed element 34, anchor element 44, compliant members 46, andshield 66 (see FIG. 1) in structural layer 24.

FIG. 12 shows a partial side view of exemplary structure 204 from FIG.10 at a subsequent stage 210 of processing. At stage 210, structurallayer 24 is patterned and etched to produce trenches 212, or spaces,between regions of structural layer 24 that will eventually become senseelectrode 28, portion 30 of sense mass 32, fixed element 34, anchorelement 44, compliant members 46, and shield 66 (see FIG. 1). Patterningand etching process techniques, such as deep reactive ion etching(DRIE), yield trenches 212 that physically separate elements 28, 30, and34, and 44 (FIG. 1) from one another. In this illustration, elements 28,30, and 34, and 44 that may be produced in structural layer 24 are notdistinguished from one another within exemplary structure 204. Rather,the light stippled patterned is used for structural layer 24 todistinguish it from the underlying sacrificial layer 50.

With reference back to MEMS device fabrication process 200 (FIG. 10),following activity 208, an activity 214 is performed. At activity 214, asacrificial layer is deposited over structural layer 24.

Referring to FIG. 13 in connection with activity 214, FIG. 12 shows apartial side view of exemplary structure 204 from FIG. 12 at asubsequent stage 216 of processing. At stage 216, a sacrificial material218 is deposited over structural layer 24 to fill trenches 212.Sacrificial material 218 is deposited such that a thickness 220 ofmaterial 218 extends above a surface 222 of structural layer 24.Sacrificial material 218 may be, for example, phosphosilicate glass(PSG). PSG is an electrically insulating material that is commonly usedas a deposition layer in semiconductor processing. Those skilled in theart will recognize that other electrically insulating materials mayalternatively be implemented.

Continuing with FIG. 14 in connection with activity 214 (FIG. 10), FIG.14 shows a partial side view of exemplary structure 204 from FIG. 13 ata subsequent stage 224 of processing. In some embodiments, sacrificialmaterial 218 may be suitably patterned and etched. As shown in FIG. 13,a region 226 of sacrificial material 218 has been etched to revealsurface 222 of structural layer 24. It will become apparent insubsequent operations that region 226 may be a location where anoverlying element (e.g., sense electrode 36 of FIG. 1) may be formed atwhich tight tolerances are required for the size of the gap (e.g., sensegap 88 of FIG. 2) between it and an underlying element (e.g., portion 30of sense mass 32 shown in FIG. 1).

Continuing with FIG. 15 in connection with activity 214 (FIG. 10), FIG.15 shows a partial side view of exemplary structure 204 from FIG. 14 ata subsequent stage 228 of processing. At stage 228, another depositionprocess may be performed to deposit additional sacrificial material 230,such as PSG, onto surface 222 of structural layer 24 at region 226 andoptionally onto sacrificial material 218. Sacrificial material 230 isdeposited at a thickness suitable for achieving a predetermined size ofthe gap. Accordingly, at stage 228, a sacrificial layer 232 which mayinclude the successive depositions of sacrificial material 218 andsacrificial material 230 is formed in accordance with activity 214 ofMEMS device fabrication process 200 (FIG. 10).

Continuing with FIG. 16 in connection with activity 214 (FIG. 10), FIG.16 shows a partial side view of exemplary structure 204 from FIG. 15 ata subsequent stage 234 of processing. At stage 234, sacrificial layer232 may then be patterned and etched to create a number of openings 236to expose regions 238 of the underlying elements. For example, openings236 may be formed to expose regions 238 of portion 30 of sense mass 32(FIG. 1) at which junctions 72, 74 (FIG. 1) are to be formed. Likewise,openings 236 may be formed to expose regions 238 of fixed element 34(FIG. 1) at which junctions 84, 86 are to be formed.

With reference back to MEMS device fabrication process 200 (FIG. 10),following activity 214, an activity 240 is performed. At activity 240,structural layer 26 (FIG. 2) is formed over sacrificial layer 232 (FIG.15) to produce at least sense elements 36, portion 38 of sense mass 32,and junctions 72, 74, 84, 86 (see FIG. 1).

Referring to FIG. 17 in connection with activity 240, FIG. 17 shows apartial side view of exemplary structure 204 from FIG. 16 at asubsequent stage 242 of processing. At stage 242, another layer ofmaterial such as polysilicon is deposited on sacrificial layer 232 toform structural layer 26. The deposition of structural layer 26 fillsopenings 236 in sacrificial layer 232 to create junctions 72, 74, 84, 86(FIGS. 1-3). FIG. 17 further shows that at stage 242, structural layer26 may be suitably patterned and etched to produce the separate elementsin structural layer 26, such as sense elements 36 and portion 38 ofsense mass 32. Interconnects (not shown) can be included as necessary.Patterning and etching process techniques of activity 240 yield spaces244 that physically separate sense elements and portion 38 from oneanother. In this illustration, elements 36 and 38, and junctions 72, 74,84, 86 are not distinguished from one another. Rather, a singlerightwardly and downwardly directed wide hatch pattern is utilized torepresent the elements of structural layer 26.

With reference back to MEMS device fabrication process 200 (FIG. 10),following activity 240, an activity 246 is performed. At activity 246,the elements in structural layers 24 and 26 are suspended over substrate22 by removing at least portions of sacrificial layers 50 and 232 byemploying, for example, one or more etching processes.

Referring to FIG. 18 in connection with activity 246, FIG. 18 shows apartial side view of exemplary structure 204 from FIG. 17 at asubsequent stage 248 of processing. At stage 248, sacrificial layer 232(FIG. 17), which may be PSG, is etched using known processes to removesacrificial material 218, 232 underlying elements (e.g., senseelectrodes 36 and portion 38 of sense mass 32, FIGS. 1-3) of structurallayer 26 and to remove sacrificial material 218 (FIG. 17) from trenches212. Although not shown, shield 66 may be suitably formed in trenches212 using a dielectric. Alternatively, shield 66 may be formed fromsacrificial material 218 (e.g., PSG) using known processes. In anexample, some of sacrificial material 218 used to form shield 66 may besuitably masked so that it remains following etching at activity 246.

Accordingly, following removal of sacrificial material 218, 232 andsense electrodes 36 and portion 38 of sense mass 32 are spaced apartfrom the underlying elements of structural layer 24, with only junctions72, 74, 84, and 86 remaining to form the structural connections, asdiscussed above in connection with FIGS. 1-3 between structural layers24 and 26. Therefore, junctions 72, 74, 84, and 86, may be referred toas “released junctions” because they are released from the surroundingsacrificial material 218, 230.

Continuing with FIG. 19 in connection with activity 246, FIG. 19 shows apartial side view of exemplary structure 204 from FIG. 18 at asubsequent stage 250 of processing. When substrate 22, sacrificial layer50, and structural layer 24 are formed as SOI wafer 206 (FIG. 10), oneor more etch processes may be performed to remove at least a portion ofthe oxide material that makes up sacrificial layer 50. Thermal oxideremoval of sacrificial layer 50 may be performed using known processesso as to release connection of the elements in structural layer 24 fromthe underlying substrate 22. Accordingly, following thermal oxideremoval, sense electrode 28, portion 30 of sense mass 32, fixed element34, anchor element 44, and compliant members 46 (FIGS. 1-3) areseparated from one another and spaced apart from surface 40 of substrate22. However, in an embodiment, sacrificial layer 50 remains at anchors42, 43, 48, and 70 (FIGS. 1-3) so that sense mass 32, anchor regions 44,fixed element 34, and shield are attached to, but suspended above,substrate 22.

The selective removal of sacrificial layers 232 and 50 can be achievedby making certain regions of structural layers 24 and 26 porous to anetch material, or etchant. This porosity may be accomplished byfabricating first and second structural layers 24 and 26 withthrough-holes (not shown for simplicity of illustration) at suitablelocations. The through-holes can provide passage through which anetchant can pass to reach the underlying sacrificial layers 232 (FIG.17) and 50. Of course, through-holes need not be fabricated through atleast structural layer 24 at the regions at which anchors 42, 43, 48,and 70 are formed so that sacrificial layer 50 that underlies thoseregions will remain following a suitably timed etching process. Thisporosity may alternatively be accomplished by the properties of thematerial used to fabricate structural layers 24 and 26. For example, theproperties of the material used to fabricate structural layers 24 and 26may be such that the etchant can permeate through the material ofstructural layers 24 and 26 to reach the underlying sacrificial layers232 and 50 without damage to structural layers 24 and 26.

With reference back to MEMS device fabrication process 200 (FIG. 9),following activity 246, MEMS device fabrication process 200 may includeother activities that are not discussed herein for brevity. Theseadditional fabrication activities, represented by ellipses, may includehermetically sealing MEMS device 20 (FIG. 1), forming electricalinterconnects, testing, and so forth. Following fabrication of MEMSdevice 20, fabrication process 200 ends with portion 38 connected toportion 30 of sense mass 32 via junctions 72, 74, and sense electrodes36 connected to fixed element 34 via junctions 84 and 86 so that the twoportions 30, 38 of sense mass 32 are in an interleaved arrangement withsense electrodes 28, 36 (FIGS. 1-3). Additionally, sense mass 32, fixedelement 34, and shield 66 are connected to and held suspended above theunderlying substrate 22 via respective anchors 48, 43, and 70.

Referring to FIG. 10, MEMS device fabrication process 100 will now bediscussed in connection with the fabrication of MEMS device 100 (FIG.6). At activity 202 of process 100, substrate 106 is provided withsacrificial layer 140 deposited thereon.

With reference to FIG. 20 in connection with activity 202, FIG. 20 showsa partial side view of another exemplary structure 252 at a beginningstage 254 of processing fabricated in accordance with MEMS devicefabrication process 200. At beginning stage 254, a substrate 256, as astarting wafer, is provided. Substrate 256 may undergo an oxidationprocess to build, or grow, an oxide layer. This oxide layer is asacrificial layer 258. Sacrificial layer 258 is represented by a darkstippled pattern and substrate 106 is represented by a light stippledpattern in FIG. 20. As will become evident in the subsequentdescription, substrate 256 will eventually become structural layer 109(FIGS. 7-9) of MEMS device 100.

Continuing with FIG. 21 in connection with activity 202, FIG. 21 shows apartial side view of exemplary structure 252 from FIG. 20 at asubsequent stage 260 of processing. In some embodiments, sacrificiallayer 258 may be suitably patterned and etched. As shown in FIG. 21,openings 262, or vias, have been formed extending through sacrificiallayer 258 to reveal a surface 264 of the underlying substrate 256. Thus,following activity 202, substrate 256 is provided with sacrificial layer258 that may be patterned and etched to form openings 262.

With reference back to MEMS device fabrication process 200 (FIG. 10),following activity 202, activity 208 is performed to form a structurallayer over the sacrificial layer to produce at least portions 110 ofsense masses 112 and sense electrodes 108 (FIGS. 7-9).

FIG. 22 shows a partial side view of exemplary structure 252 from FIG.21 at a subsequent stage 266 of processing. As shown in FIG. 22,structural layer 107 in the form of, for example, polysilicon, isdeposited over sacrificial layer 258. Deposition of the polysiliconstructural layer 107 fills openings 262. Structural layer 107 may besuitably patterned and etched. As shown, openings 268 have been formedextending through structural layer 107 to reveal a surface 270 of theunderlying sacrificial layer 258. Thus, following activity 208,structural layer 107 is deposited and processed to include openings 268that physically separate elements 108 and 110 (FIGS. 6-9) from oneanother. In this illustration, elements 108 and 110 that may be producedin structural layer 107 are not distinguished from one another withinexemplary structure 252. Rather, the rightwardly and downwardly directedwide hatching is used for structural layer 107 to distinguish it fromthe underlying sacrificial layer 140.

Referring briefly to MEMS device fabrication process 200 (FIG. 10),following activity 208, activity 214 is performed to deposit asacrificial layer over structural layer 107.

FIG. 23 shows a partial side view of exemplary structure 252 from FIG.22 at a subsequent stage 272 of processing. At stage 272, a sacrificialmaterial, such as an oxide, is deposited over structural layer 107. Aswill become evident in the subsequent description, this sacrificialmaterial will eventually be sacrificial layer 140 (FIGS. 7-9) of MEMSdevice 100. Sacrificial material 140 may be of sufficient thickness tofill openings 264.

Again, referring briefly to MEMS device fabrication process 200 (FIG.10), following activity 214, activity 240 is performed to form anotherstructural layer.

FIG. 24 shows a partial side view of exemplary structure 252 from FIG.23 at a subsequent stage 274 of processing. At stage 274, the structureformed at stage 272 (FIG. 23 is flipped and bonded to a substrate. Inthis exemplary embodiment, the substrate is substrate 106 of MEMS device100 (FIG. 6).

Continuing with FIG. 25 in connection with activity 240, FIG. 25 shows apartial side view of exemplary structure 252 from FIG. 24 at asubsequent stage 276 of processing. At stage 276, structural layer 109is processed by, for example, grinding, patterning, and etching to format least portions 116 of sense masses 112, sense elements 114, anchorelements 120, and so forth (FIGS. 6-9). Patterning and etching processtechniques, such as deep reactive ion etching (DRIE), yield trenches 278that physically separate elements 116, 114, and 120 from one another. Inthis illustration, elements 116, 114, and 120 that may be produced instructural layer 109 are not distinguished from one another withinexemplary structure 252. Rather, the light stippled patterned is usedfor structural layer 109 to distinguish it from the underlyingsacrificial layer 258. Thus, following activity 240 (FIG. 10), elements116, 114, and 120 have been formed and are physically separated from oneanother.

Referring briefly to MEMS device fabrication process 200 (FIG. 10),following activity 240, activity 246 is performed to suspend the variouselements of MEMS device 100 (FIG. 6) formed in structural layers 107 and109 by removing at least portions of sacrificial layers 258 and 140.

FIG. 26 shows a partial side view of exemplary structure 252 from FIG.25 at a subsequent stage 280 of processing. At stage 280, sacrificiallayers 258 and 140 are etched using one or more known processes toremove sacrificial material 140, 258 underlying certain elements (e.g.,sense electrodes 108 and 114, portions 110 and 116 of sense masses 112,and so forth). Accordingly, following removal of sacrificial material140, 258, sense electrodes 114 and portions 116 of sense masses 112 arespaced apart from the underlying elements of structural layer 107.Additionally, portions 110 of sense masses 112 are spaced apart from theunderlying substrate 106. However, junctions 144 remain to form thestructural connections between portions 110 and 116 of sense masses 112,as discussed above in connection with FIGS. 6-9. Therefore, junctions144 may be referred to as “released junctions” because they are releasedfrom the surrounding sacrificial material 140, 258.

Although particular system configurations are described in conjunctionwith FIGS. 11-26, above, embodiments may be implemented in systemshaving other architectures, as well. Furthermore, it is to be understoodthat certain ones of the process blocks depicted in FIG. 10 may beperformed in parallel with each other or with performing otherprocesses. In addition, it is to be understood that the particularordering of the process blocks depicted in FIG. 10 may be modified,while achieving substantially the same result. Accordingly, suchmodifications and other variations are intended to be included withinthe scope of the inventive subject matter.

Thus, various embodiments of a MEMS device having vertical sensingcapability and methods of fabrication have been described. The MEMSdevices include two structural layers, and junctions connecting elementsof the two structural layers. The two structural layers are subsequentlymechanically released, or detached, from the underlying substrate.Accordingly, a movable sense mass (a portion of which is formed in eachof the two structural layers) is interleaved both below one fixedelectrode and above a separate fixed electrode. This enablesdifferential sensing such that any signal component resulting from thecommon mode displacement will effectively cancel. Methodology entailsfabricating the MEMS device using two structural layers, in whichportions of the two structural layers are not in direct contact with theunderlying substrate, and in which each structural layer has sensecapability of an opposing polarity so as to provide a differentialconfiguration.

An embodiment of a MEMS device comprises a substrate, and a firstelement and a second element formed in a first structural layer. Thefirst element is fixedly coupled with the substrate, and the secondelement is suspended over the substrate. The MEMS device furthercomprises a third element and a fourth element formed in a secondstructural layer. The third element is spaced apart from the secondelement in a direction perpendicular to a surface of the substrate, andthe fourth element is spaced apart from the first element in thedirection. A junction is formed between the second element and thefourth element, the junction coupling the fourth element with the secondelement.

An embodiment of a method for fabricating a MEMS device is alsodisclosed. The method comprises forming a first structural layer on afirst sacrificial layer overlying a substrate to produce first andsecond elements separated from one another, depositing a secondsacrificial layer over the first structural layer, and forming a secondstructural layer over the second sacrificial layer to produce third andfourth elements separated from one another. The method further comprisesforming at least one junction between the second element and the fourthelement and suspending the second, third, and fourth elements over thesubstrate by removing at least portions of the first and secondsacrificial layers, wherein the third element is spaced apart from thesecond element in a direction perpendicular to a surface of thesubstrate, the fourth element is spaced apart from the first element inthe direction, and the fourth element is coupled with the second elementvia the at least one junction.

While the principles of the inventive subject matter have been describedabove in connection with specific systems, apparatus, and methods, it isto be clearly understood that this description is made only by way ofexample and not as a limitation on the scope of the inventive subjectmatter. The various functions or processing blocks discussed herein andillustrated in the Figures may be implemented in hardware, firmware,software or any combination thereof. Further, the phraseology orterminology employed herein is for the purpose of description and not oflimitation.

The foregoing description of specific embodiments reveals the generalnature of the inventive subject matter sufficiently so that others can,by applying current knowledge, readily modify and/or adapt it forvarious applications without departing from the general concept.Therefore, such adaptations and modifications are within the meaning andrange of equivalents of the disclosed embodiments. The inventive subjectmatter embraces all such alternatives, modifications, equivalents, andvariations as fall within the spirit and broad scope of the appendedclaims.

What is claimed is:
 1. A microelectromechanical systems (MEMS) device comprising: a substrate; a first element and a second element formed in a first structural layer, said first element being fixedly coupled with said substrate, and said second element being suspended over said substrate; a third element and a fourth element formed in a second structural layer, said third element being spaced apart from said second element in a direction perpendicular to a surface of said substrate, and said fourth element being spaced apart from said first element in said direction; and a junction formed between said second element and said fourth element, said junction coupling said fourth element with said second element.
 2. A MEMS device as claimed in claim 1 further comprising: an anchor attached to said substrate; and a compliant member interconnected between said second element and said anchor to allow concurrent movement of said second and fourth elements relative to said substrate.
 3. A MEMS device as claimed in claim 2 wherein said compliant member is connected at an outer edge of said second element such that said second element is a cantilevered structure.
 4. A MEMS device as claimed in claim 2 wherein said compliant member enables rotational movement of said second and fourth elements about an axis of rotation that is offset away from said second element.
 5. A MEMS device as claimed in claim 1 wherein said second element includes an opening extending through a thickness of said second element, and said first element resides in said opening.
 6. A MEMS device as claimed in claim 5 wherein said opening extends laterally from an outer edge of said second element such that said second element is a U-shaped member.
 7. A MEMS device as claimed in claim 5 wherein said junction comprises: a first junction element positioned at a first side of said opening; and a second junction element positioned at a second side of said opening, said first and second junction elements coupling said fourth element with said second element so that said fourth element spans across a width of said opening.
 8. A MEMS device as claimed in claim 1 further comprising a shield interposed between said first element and said second element, said shield being configured to electrically isolate said first element from said second element.
 9. A MEMS device as claimed in claim 8 further comprising a shield anchor attached to said substrate and coupled to said shield so that said shield is suspended over said substrate.
 10. A MEMS device as claimed in claim 1 wherein said junction is a first junction, and said MEMS device further comprises: a fifth element formed in said first structural layer and fixedly coupled with said substrate; and a second junction formed between said third element and said fifth element, said second junction coupling said third element with said fifth element.
 11. A MEMS device as claimed in claim 10 wherein: said fifth element is displaced away from said first and second elements in a lateral direction that is approximately parallel to a surface of said substrate; and said MEMS device further comprises a shield interposed between said fifth element and said first and second elements, said shield being configured to electrically isolate said fifth element from said first and second elements.
 12. A MEMS device as claimed in claim 1 wherein: said second and fourth elements form a movable sense mass; said first element is a first fixed sense electrode, wherein a first sense signal is produced between said first fixed sense electrode and said fourth element in response to movement of said sense mass; and said third element is a second fixed sense electrode, wherein a second sense signal is produced between said second fixed sense electrode and said second element in response to said movement of said sense mass, said second sense signal being opposite in polarity from said first sense signal.
 13. A microelectromechanical systems (MEMS) device comprising: a substrate; a first element and a second element formed in a first structural layer, said first element being fixedly coupled with said substrate, and said second element being suspended over said substrate; a third element and a fourth element formed in a second structural layer, said third element being spaced apart from said second element in a direction perpendicular to a surface of said substrate, and said fourth element being spaced apart said first element in said direction; a first junction formed between said second element and said fourth element, said first junction coupling said fourth element with said second element; an anchor attached to said substrate; a compliant member interconnected between said second element and said anchor to allow concurrent movement of said second and fourth elements relative to said substrate; a fifth element formed in said first structural layer and fixedly coupled with said substrate; and a second junction formed between said third element and said fifth element, said second junction coupling said third element with said fifth element.
 14. A MEMS device as claimed in claim 13 wherein said compliant member is connected at an outer edge of said second element such that said second element is a cantilevered structure, and said compliant member enables rotational movement of said second and fourth elements about an axis of rotation that is offset away from said second element.
 15. A MEMS device as claimed in claim 13 further comprising a shield interposed between said first and second elements, said shield being configured to electrically isolate said first element from said second element.
 16. A microelectromechanical systems (MEMS) accelerometer comprising: a substrate; a first electrode and a first portion of a movable sense mass formed in a first structural layer, said first electrode being fixedly coupled with said substrate, and said first portion of said movable sense mass being suspended over said substrate; a second electrode and a second portion of said movable sense mass formed in a second structural layer, said second electrode being spaced apart from said first portion of said movable sense mass in a direction perpendicular to a surface of said substrate, and said second portion of said movable sense mass being spaced apart from said first electrode in said direction; and a junction formed between said first and second portions of said movable sense mass, said junction coupling said second portion of said movable sense mass with said first portion of said movable sense mass.
 17. A MEMS accelerometer as claimed in claim 16 further comprising: an anchor attached to said substrate; and a compliant member interconnected between said first portion of said movable sense mass and said anchor to allow concurrent movement of said first and second portions of said movable sense mass relative to said substrate.
 18. A MEMS accelerometer as claimed in claim 17 wherein said compliant member is connected to an outer edge of said first portion of said movable sense mass such that said second portion of said movable sense mass is a cantilevered structure, said compliant member enabling rotational movement of said first and second portions of said movable sense mass about an axis of rotation that is offset away from said first portion of said movable sense mass.
 19. A MEMS accelerometer as claimed in claim 16 wherein: said first portion of said movable sense mass includes an opening extending through a thickness of said first portion; said first electrode resides in said opening; and said junction comprises a first junction element positioned at a first side of said opening, and a second junction element positioned at a second side of said opening, said first and second junction elements coupling said second portion of said movable sense element with said first portion of said movable sense element so that said second portion of said movable sense element spans across a width of said opening and is suspended over said first electrode.
 20. A MEMS accelerometer as claimed in claim 16 wherein said junction is a first junction, and said MEMS accelerometer further comprises: a fixed element formed in said structural layer and fixedly coupled with said substrate, said fixed element being displaced away from said first portion of said movable sense mass and said first electrode in a lateral direction that is approximately parallel to a surface of said substrate; and a second junction formed between said second electrode and said fixed element such that said second electrode is a cantilevered structure suspended over said first portion of said movable sense mass. 